help

two weeks ago i posted a thread about my leaves curling and changing colour from the center
i was advised to cut down watering and nute as they were only seedling and to have my ph at 5.5
i did the above i cut the nutes right out so now it only getting water my ph in my tub is 5.5 and i let it get to 6.0 before i drop it back down and i water them on mondays and thursdays they started to come good getting there colour back.
i didnt check them from last friday till the monday and in them days thay started going brown at the tips and drying out and the leaves a getting lighter again though this time the light is on the out side of the leaves when last time they were changing from the center of thr leaves